In recent decades, the variety and flexibility of audio applications has increased immensely with e.g. the variety of audio and capture rendering applications varying substantially. The audio rendering and capture setups are used in diverse acoustic environments and for many different applications.
In many applications it is therefore desirable to be possible to determine the position of a microphone, a listening position or a loudspeaker relative to other loudspeakers. In many applications these issues may be reduced to the same underlying problem, namely that of determining a position of a microphone.
Indeed, in many applications, a listening position may be determined by calibrating the system using a microphone which is positioned at the listening position. Similarly, speaker positions may be determined by positioning a microphone at a speaker position, or perhaps by permanently implementing a microphone in a loudspeaker. A particularly important challenge in many applications is that of determining loudspeaker positions for a rendering setup, such as for a surround sound system.
Indeed, a significant inconvenience perceived by consumers when using e.g. home cinema surround sound is the need for a relatively large number of speakers to be positioned at specific positions. Typically, practical surround sound speaker setups will deviate from the ideal setup due to users finding it impractical to position the speakers at the optimal positions. Therefore, real setups may deviate substantially from the ideal setup, and accordingly procedures for calibrating the rendering systems and compensating for imperfections have been developed. Flexible systems based on speaker calibration have been developed to provide flexible setups where users may position speakers relatively freely at convenient positions with the system automatically adjusting the audio processing and rendering to the specific setup.
Such systems may be based on determining the relative positions of the speakers. For example, WO 2006/131893-A1 discloses an automatic calibration of a multichannel system based on a system where each loudspeaker is equipped with a microphone to allow impulse responses to be determined from each pair-wise loudspeaker combination. This information is then used to determine the relative locations of the loudspeakers. An optimization procedure is then used to distribute the multi-channel audio signals such that an optimum listening experience, as defined in the ITU-R BS.775-1 recommendations, is obtained at a specified listening position. In U.S. Pat. No. 5,666,424-A, a calibration procedure using a microphone at the listening position is performed to determine the relative distance from each loudspeaker to the listening position.
Existing rendering calibrations are mostly based on a loudspeaker rendering a specific test or probe signal, such as noise sequences or chirp sounds, with the resulting signals being captured by a microphone. The calibration of such systems may take several seconds. More importantly, the process relies on specific audio test signals and therefore cannot be performed during the normal operation of the audio system, such as during music playback.
However, it is desirable to be able to determine positions during normal use of a rendering system, such as during music rendering. This may typically provide an improved determination which allows a continuous adaptation of the system. For example, the system may automatically adapt to a user moving a speaker during play-back. This may be particularly significant in many current and future systems using portable and fully wireless battery-powered loudspeakers which are becoming increasingly popular.
However, normal audio tends to vary substantially with the specific instantaneous properties being unpredictable. Therefore, position estimation based on such signals tend to often result in relatively unreliable estimates. Furthermore, the signals from different loudspeakers tend to be different from each other, but with the difference at any given time being unknown.
Hence, an improved approach for determining a position of a microphone would be advantageous and in particular an approach allowing for increased flexibility, automatic determination, reduced reliance on specific test signals, improved estimation accuracy and/or improved performance would be advantageous.